Field of the Invention
The present invention relates to a white heat-curable epoxy resin composition that has a high strength and toughness, and is superior in heat resistance property, an optical semiconductor element case made of the white heat-curable epoxy resin composition and a semiconductor device whose light receiving element and other semiconductor elements are encapsulated by a cured product of such composition.
Background Art
Optical semiconductor elements such as LEDs (Light Emitting Diode) have come into use as various indicators and light sources such as displays on the streets, automobile lamps and residential lightings. Among such LEDs, white LED products are being developed rapidly in various fields under the sloganizing keywords of reduction of carbon dioxide and saving of energies.
As one of materials for semiconductor and electronic devices such as LEDs, a polyphthalamide resin (PPA) has been widely used at present for the material of a photoreflector. Reflector materials using PPA are advantageous in that they have a high strength and flexibility. In recent years, however, as a result of optical semiconductor devices having a progressively higher output and shorter wavelength, PPA has become unadaptable thereto due to a reduction of the optical output being induced by a violent severe deterioration such as a change in color when used around optical semiconductor elements (see JP-A-2006-257314).
JP-B-2656336 discloses an optical semiconductor device using, as an optical semiconductor encapsulating resin, a B-stage epoxy resin composition comprised of an epoxy resin, a curing agent and a curing accelerator, serving as encapsulation resin composition for optical semiconductor elements, and having a cured body of the resin composition in which the foregoing constituents are uniformly mixed on a molecular level. This composition mainly uses a bisphenol A-type epoxy resin or a bisphenol F-type epoxy resin as the epoxy resin. Though JP-B-2656336 also discloses that triglycidyl isocyanate or the like may be used, triglycidyl isocyanate is added in small amounts to the bisphenol type epoxy resin in the working examples, and examinations by the inventors of the present invention show that there has been a problem that such B-stage epoxy resin composition for encapsulating the semiconductor turns yellow particularly when left under a high temperature for a long time.
JP-A-2000-196151 discloses an LED encapsulated by an alicyclic epoxy resin obtained by oxidizing a cyclic olefin. JP-A-2003-224305 discloses an epoxy resin composition for encapsulating a light-emitting element containing a triazine derivative epoxy resin and an acid anhydride curing agent. JP-A-2005-306952 discloses an epoxy resin composition for encapsulating a light-emitting element containing: (A) an epoxy resin containing a hydrogenated epoxy resin, a triazine ring-containing epoxy resin and an alicyclic epoxy resin obtained by epoxidizing a cyclic olefin; and (B) an epoxy resin composition for encapsulating a light-emitting element containing an acid anhydride curing agent. The epoxy resin compositions for encapsulating the light-emitting element of the JP-A-2000-196151, JP-A-2003-224305 and JP-A-2005-306952 also failed to provide sufficient solutions to the problem of yellow discoloration that takes place when left under a high temperature for a long time.
Though JP-A-2000-196151, JP-A-2003-224305 and JP-A-2005-306952 refer to the use of triazine derivative epoxy resins for the epoxy resin compositions for encapsulating a light-emitting element, any of them uses the triazine derivative epoxy resin and an acid anhydride, and there have been pointed out the problem that when they are used as a reflector for LED backlight installed in a modern flat-panel TV, the reflector may be destroyed due to lack of strength and toughness since the reflector is ultraminiaturized and highly reduced in thickness.
In order to solve such problems, there are proposed some epoxy resin compositions for semiconductor in which the acid anhydride is denatured by a linker or an acid anhydride having flexibility is used, as disclosed in JP-A-2013-100440 and JP-A-2014-95051. It has been, however, not possible to realize such composition that satisfies all of the strength, toughness and heat resistance property since a part thus denatured and a framework having a flexibility itself have a comparatively low heat resistance property, as well as a comparatively low reliability with respect to heat or light.